I started with a Torklift receiver on my chassis cab. you can see the side plates run from the rear spring hangers all the way to the end of the frame rails. This is what keeps it from twisting when you put an extension on it.
My lower boxes are 36x18x18 and held by six bolts going through dual 18" long brackets welded to the cross members of the deck. When I had my shorter camper loaded, I could only access the boxes if I removed the jacks or removed the camper. Yours looks like a 84" CA model,so you can go with longer boxes but will have the same obstruction to access as I did.
This was fixed once I bought the larger camper. I have to lower the jack feet so they clear the door, but now have full access.
I used two 48x18x18 boxes on each side that are bolted down to the deck. If I kept the shorter Arctic Fox, I would have had to use to shallower boxes due to the floor extension above the wheel wells. My Host does not have this, which is why I waited to install boxes until I had my larger camper.
My deck is 8' wide on the outside of the rub rails and so are both my campers. with no upper boxes, it was easy to use the short turnbuckles to the deck's stake pockets welded into the rub rails. Although I inset the boxes past the stake pockets, I could not get suffient angle to lock and unlock the turnbuckle until I added eyelets to to the outside of the rub rail.
The turnbuckles prevent access to the upper boxes unless removed, so I chose the quick release short range FastGun. When locked it is a second level of security for contents in my upper boxes which have two point locking doors.
